A fresh investigation into the disappearance 33 years ago of a little boy named Etan Patz led today to the Manhattan basement workshop of a handyman named Othneil Miller.

Investigators believe that Patz, who was 6 years old when he vanished in 1979, was in Miller's basement the night before he disappeared when Miller befriended the boy and gave him a dollar, sources told ABC News.

Federal agents and New York City police began to tear up the concrete floor of the basement at 127 Prince St. in the SoHo section of Manhattan. The basement was Miller's workshop in 1979.

Patz's disappearance as he walked to the bus stop alone for the first time in his young life has haunted the city. The search for Patz has been one of the largest, longest lasting and most heart wrenching hunts for a missing child in the country's recent history.

The new investigation is also reexamining the decades old assumption that Patz was abducted by convicted pedophile Jose Ramos. Ramos, now in prison for an unrelated case, was never charged with Patz's abduction.

Today's probe, which was reopened by Manhattan District Attorney Cyrus Vance in 2010, began with an interview of Miller.

Based on that interview, law enforcement sources said, a dog was brought to the scene as a warrant was drawn up. The cadaver dog got a positive hit for possible human remains. The warrant was served and the preparations for digging began.

On Thursday night, Paul Browne, NYPD deputy commissioner for public information, confirmed that Miller had made statements to police, and that a cadaver dog got positive hits at the scene. However, Browne said the dog hits came before the Miller interview, not after.

FBI agents today, some in raid jackets and others in white or blue T-shirts marked "Evidence Response Team," brought out cameras, crow bars and other equipment.

The preparations for the search included mapping the basement, making sketches, taking photographs and other procedures for collecting evidence.

Browne provided a recap of the day's events Thursday evening:

"The way we left it this evening, we began a little bit of digging in the north wall at the very end of the long basement area," he said. "It's 13-by-62 feet. At the very end of it, a dig has begun just off the wall.

"That's where it was left off tonight," Browne said. "Kind of makes sense to work from the back out towards the front as we remove material."

On Friday, Browne said, "You'll see dumpsters on the street here where, as we go through material, it will be moved into the dumpsters, will be moved to a landfill and isolated there [in case the material is needed later]."

The excavation is expected to last five days.

For Stu Grabois, the assistant U.S. attorney who spent 27 years on the case, it was good news to hear of the new probe.

"I am pleased that Cy Vance is exploring everything that can help to bring justice to the Patz family," said .

According to sources, the area of the basement where the dog picked up the scent appears to be one that had been resurfaced with fresh concrete at or shortly after the time of Patz's disappearance.

Sources told ABC News that even if a body had been kept for 24 hours or less and then moved, a trained dog could pick up the scent decades later.

The basement was searched in 1979, the year the boy disappeared, but the floor was never dug up.

Since then, drywall has been put up over the room's brick walls. The drywall will be removed and the bricks examined and tested for blood evidence using advanced forensic techniques that were not available three decades ago, officials said.

The floor will also be dug up in a search for human remains, clothing or other evidence.

Current forensics will allow authorities to look into hollows and to perform sophisticated DNA analysis on any potential evidence.

"It's a joint FBI-NYPD search for human remains clothing or personal effects," Browne told reporters outside the building after investigators entered using a search warrant.

Patz vanished on May 25, 1979 in the SoHo neighborhood of Manhattan while walking alone to a school bus stop for the first time.